Sweet potatoes have been an important staple in the Hawaiian diet for centuries, but farmers trying to grow the crop organically face huge challenges ranging from pests to pathogens that can reduce their yield to less than 20%.

There are many boots in the soil working to find solutions to support local organic farms and protect uala ownership for Native Hawaiians.

Six researchers at the University of Hawaii Manoa have even discovered two new and promising Hawaiian sweet potato varieties that matched or outperformed a local favorite: the purple Okinawa sweet potato.

Considering Hawaii’s high demand for sweet potatoes, there’s a huge opportunity to produce revenue, one of the UH researchers, Michael Kantar, explained.

Referencing universities doing similar projects with other crops like honey crisp apples generating over $14 million for the University of Minnesota and strawberry varieties bringing $37 million to the University of California Davis, Kantar said they could do something similar at UH.

Kantar’s colleague Ted Radovich explained that they did not intentionally breed the sweet potatoes for their study. The University of Hawaii has certified organic plots at the research center where they preserve traditional Hawaiian heritage crops.

Once they noticed their sweet potato Mohihi yielded 50 seedlings, they decided to conduct a research study that could help increase yield and economic value for future farmers.

Between 2018 and 2019, researchers selected 12 of the 50 varieties and planted them in different climates: fall in Waimanalo in 2018, and spring in Poamoho and Waimanalo in 2019.

After harvest, they collected yield metrics, root shape, damage susceptibility, color, and sucrose content, analyzing success by comparing them to the Okinawa sweet potato; they found one variety that outperformed and another that matched the favorable qualities of the Okinawa.

The results of the study were published in Agronomy in June 2021.

“When you take a cutting, you’re just cloning that mother plant, but when the conditions are right, there’s nothing that prevents it from crossing with another genetically distinct individual,” Kantar said.

Sweet potatoes have about 50,000 genes, nearly double the number of genes present in humans, Kantar explained.

They also have six versions of a single gene, resulting in an endless number of possible varieties.

So far, the study has named 19 potential pollen parents and temporarily nicknamed the 12 varieties as “Hapa Mohihi,” or HM.

They also planted four others for comparison — the commercial standard Okinawa sweet potato, the traditional Hawaiian variety prevalent among Molokai homesteaders, Lanikeha, the popular Big Island variety, Kahanu Purple and the maternal parent Mohihi.

After evaluation, HM-34 and HM-26 showed the most potential for successful sale at the market.

“We wanted to identify the best potatoes, and then turn it over to the community to decide if they want them released, what names they want to give them, and then how they will be distributed,” Radovich said.

The next phase will be harvesting the favorable HMs in Poamoho in the spring and sharing them with community members through the nonprofit Ke Kula Nui O Waimanalo — of which Radovich is a board member — to include community voices to decide if they would like to name the varieties and sell them commercially.

History And Biopiracy

Sweet potatoes and other popular local staples can play a big role in efforts to diversify Hawaii’s food sources and reduce its dependence on imports.

“We want to protect them and we want to make them available to people who want to grow them.” — University of Hawaii researcher Ted Radovich

Explaining the significance of indigenous crops, Noa Lincoln, UH assistant professor of indigenous crops, posed a question that his mentor often asked, “When did Hawaiians become Hawaiian?”

He answered that it wasn’t until people interacted with the land, adapting different practices and creating new crops.

About 105 crops make up 95% of the global food intake, neglecting and underutilizing approximately 3,000 crops and 30,000 edible plants — largely belonging to indigenous peoples — according to Lincoln.

“We’re only using a sliver of the potential food diversity out there,” he said, explaining that widening the scope of crops consumed would increase food security.

Unlike foods that are mass-produced in factories, Lincoln argued that cultural preservation and proper food patenting — ownership of the original product — depended on the documentation of indigenous plant varieties.

Regulating the co-opting of cultural concepts, traditions and crops often does not exist, despite the United Nations Declaration on the Rights of Indigenous Peoples indicating the right to indigenous ownership of traditional medicine, plants, animals and minerals, Lincoln said.

For centuries, non-Hawaiian companies have grown indigenous varieties of crops like kalo or taro, ko or sugarcane and awa or kava, marketing products using native peoples’ storylines and making profits that do not give back to Hawaiian communities.

The sweet potato played an integral role in the diets of Hawaii’s early Polynesian settlers, having arrived as a canoe crop sometime after 1300 CE, spurring population growth, especially in Leeward districts.

Hawaiians developed about 250 different varieties of uala or sweet potato, according to a separate 2018 study on Hawaiian ancestral crops that Lincoln co-authored with six other researchers. However, between 1778 and 1900, when foreign disease decimated the Native Hawaiian population, most dryland field systems were abandoned or used for cattle.

In the 1990s, approximately 1,100 acres were in cultivation and generated $7.3 million, compared to just $1.8 million and less than 500 acres recorded in 2016.

The Organic Challenge

But a healthy batch of organic sweet potatoes can have huge rewards. Growers can receive retail price premiums ranging from 9%–100% for organic vegetables, increasing their return on investments, the 2021 sweet potato study noted.

And according to the Hawaii Department of Agriculture, organic food sales rose from $6 million to $15 million between 2012 and 2017 in Hawaii, and nationally increased 31% in three years.

Nematologist Koon-Hui Wang explained that to support organically grown indigenous crops, farmers need to go against commercial farming practices that deplete soil nutrients, disturb soil health, increase greenhouse gas emissions, and decrease biodiversity in soil.

Wang said sweet potato weevil, rough sweet potato weevil, root-knot and reniform nematodes can cause more than an 80% yield loss.

The weevil is the most serious worldwide pest of sweet potatoes, causing root malformation and a bitter taste.

In 2019, during their final harvest for the study, researchers lost all their potatoes in Waimanalo due to weevil infestation. So Wang will be working with other researchers over the next three years to develop cost-effective solutions to prevent weevil damage for organic farmers.

At Kualoa Ranch, diversified agriculture and small livestock manager Austin Tom plants one row of sweet potatoes per week to keep harvesting manageable once the potatoes are ready.

He said the planting process is simple: “Basically, you just cut this (clipping) and then you’ll remove all the leaves so it doesn’t lose as much water during transplant. And then you just shove it in a hole and then that’s it.”

To avoid pests while keeping the crops organic, Tom grows sunn hemp for about two months, then kills the plant and buries it in the ground where it releases monocrotaline that destroys pests in the soil. Then the sweet potatoes are planted, he said.

But Wang said sunn hemp is not perfect and can often deplete good nutrients in the soil as well. Her next research endeavor is to promote an organic farming system that uses ecologically-based pest controls and biological fertilizers derived largely from nitrogen-fixing or carbon-fixing cover crops.

While the sweet potato research is nowhere near complete, researchers are using their findings to support local organic farms, collaborate with the community and bring Hawaiian sweet potato ownership back to native people.

“We want to protect them and we want to make them available to people who want to grow them,” Radovich said.

“Hawaii Grown” is funded in part by grants from the Ulupono Fund at the Hawaii Community Foundation, the Marisla Fund at the Hawaii Community Foundation, and the Frost Family Foundation.